Rates of women who are opting for preventive mastectomies, such as Angeline Jolie, have increased by an estimated 50 percent in recent years, experts say. But many doctors are puzzled because the operation doesn't carry a 100 percent guarantee, it's major surgery -- and women have other options, from a once-a-day pill to careful monitoring.

"It's a well-known pattern," said lead researcher Frank Stafford, an economist at University of Michigan's Institute for Social Research. "Men tend to work more outside the home, while women take on more of the household labor."

He points out individual differences among households exist. But in general, marriage means more housework for women and less for men. "And the situation gets worse for women when they have children," Stafford said.

Overall, times are a' changing in the American home. In 1976, women busied themselves with 26 weekly hours of sweeping-and-dusting work, compared with 17 hours in 2005. Men are pitching in more, more than doubling their housework hours from six in 1976 to 13 in 2005.
Science confirms obvious

Stafford analyzed time-diaries and questionnaires from a nationally representative sample of men and women over a 10-year period between 1996 and 2005. The federally-funded study showed that, compared with the single life, marriage meant more housework for both men and women.

"Marriage is no longer a man's path to less housework," Stafford said.

Single women in their 20s and 30s did the least housework, about 12 weekly hours, while married women in their 60s and 70s did the most — about 21 hours a week.

Men showed a somewhat different pattern, with older men picking up the broom more often than younger men. Single guys worked the hardest around the house, trumping all age groups of married men.

Having kids boosts house chores even further. With more than three kids, for instance, wives took on more of the extra work, clocking about 28 hours a week compared with husbands' 10 hours.